Process for producing a homogeneous polyethylene material in the presence of a catalyst

ABSTRACT

The present invention concerns a process for producing homogeneous polyethylene materials and processes for making high density, medium density and low density films therefrom. The process involves producing a polyethylene composition in a multistage reaction sequence of successive polymerization stages in the presence of an ethylene-polymerizing catalyst system. According to the invention, the process is carried out using an unsupported catalyst having magnesium and titanium as active constituents, in at least one loop polymerization stage and at least one gas phase polymerization stage and, operated with different amounts of hydrogen and comonomers to produce a high molecular weight portion in one of the polymerization stages and a low molecular weight portion in another so as to provide a polyethylene composition with the low molecular weight part having a MFR 2  of 250 g/10 min or more. With this process it is possible to obtain homogeneous bimodal polyethylene material.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/FI99/00392 which has an Internationalfiling date of May 10, 1999, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a process for polymerising ethylene intwo or more stages to produce a homogeneous polyethylene material thatis advantageously used in film-making. More particularly, the inventionrelates to a process comprising a loop and a gas phase reactor, wherethe material has a good homogeneity and the fines level of the polymerpowder is low.

BACKGROUND OF THE INVENTION

A number of processes designed to produce bimodal polyethylene are knownin the art. Processes comprising two or more cascaded slurry reactorsare known to produce homogeneous polyethylene materials having a goodprocessability in the end use applications. However, these processeshave a limitation of only being able to produce bimodal polyethyleneshaving a relatively high density, higher than about 935 kg/m³.

On the other hand, processes disclosing the use of two or more cascadedgas phase reactors are also known in the art. These processes have theadvantage of being able to produce polyethylenes over a wide densityrange. However, the homogeneity and processability of the materialsproduced in these processes and which are available on the market havenot been on such a level that they could seriously compete with thematerials produced in the processes comprising cascaded slurry reactors.

A process comprising a cascade of a loop and a gas phase reactor is alsoknown in the art. While this kind of a process can successfully be usedto produce polyethylenes with a fairly good balance betweenprocessability and homogeneity over a fairly broad density range, theyhave occasionally shown problems to produce very demanding materialshaving a good homogeneity. Typical examples of such materials arebimodal film materials, especially bimodal high density film material.Also high density pipe materials can be included into this productcategory.

DESCRIPTION OF RELATED ART

Processes to produce bimodal materials for high density PE film areknown from e.g. EP-B-517868, EP-A-691353 and WO-A-9618662.

EP-B-517868

The patent discloses a process for producing bimodal polyethylene in aloop and a gas phase reactor. The publication teaches the use ofdifferent inert hydrocarbons as a diluent in the loop reactor, but itstates that propane, especially in supercritical conditions, ispreferred. The publication does not refer to the homogeneity of the filmmaterial nor does it discuss the possibilities to reduce the level ofthe fine polymer particles. Silica based catalyst has been used in allexamples.

WO-A-9618662

The patent application discloses a process comprising at least two loopreactors and at least one gas phase reactor. It also teaches thepreparation of material to be used in HD film applications. Again, thepublication mentions that different inert hydrocarbons can be used as adiluent in the loop reactor, but that specifically propane especially insupercritical state is preferred. The document discusses both thehomogeneity of the film material and the level of fine polymer, andteaches that the homogeneity can be improved and the fines level can bereduced by installing a prepolymeriser in the process. Also thisdocument discloses only the use of silica-supported catalysts.

EP-A-691353

The patent application discloses a process for producing an in situblend of ethylene polymers giving a low gel film. The process comprisestwo gas phase reactors. A low MFR copolymer is made in the first reactorand a high MFR copolymer is made in the second reactor.

EP-A-754708

The patent application discloses a process for producing an in situpolyethylene blend. The modality of the polymer is increased by addinginto the first reactor a saturated alicyclic hydrocarbon, which isliquid at process conditions. The addition of the saturated alicyclichydrocarbon reduced the gel level of the film made of the polymer.

The document also discloses that the gas phase processes have problemswith the resulting material having a too high level of gels comparedwith slurry or solution processes. Further, it reveals that the gasphase resins exhibit significant compositional, molecular andrheological heterogeneities. The use of a non-supported catalyst isdisclosed in the document.

U.S. Pat. No. 4,859,749

The patent discloses a two stage polymerization process of ethylene,which uses a catalyst which consists of (a) a transition metal componentwhich is the reaction product of magnesium alcoholate with a chlorinecontaining titanium compound and a chlorine containing organoaluminumcompound and (b) organoaluminum cocatalyst. The examples disclose that ahomogeneous material in a two stage slurry process has been obtained.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a process forproducing polyethylene materials over a wide density range with goodprocessability in the end use applications and an excellent homogeneity.In particular, it is an aim to provide a process for producinghomogeneous polyethylene film and pipe materials having a goodprocessability.

It is a further objective of the invention to provide a film-makingprocess.

These and other objects, together with the advantages thereof over knownprocesses and products, which shall become apparent from thespecification which follows, are accomplished with the invention ashereinafter described and claimed.

According to the present invention, bimodal polyethylene materialshaving a very broad molecular weight distribution are prepared in atleast two of the stages in a process comprising a cascade of one or moreloop reactor(s) and one or more gas phase reactor(s). The invention isbased on the surprising finding that the homogeneity of the material canbe improved by performing the polymerization in the presence of aspecific catalyst. The catalyst is unsupported and comprises titaniumand magnesium as active constituents.

The homogeneous material is produced by polymerizing or copolymerizingethylene in the presence of a ethylene-polymerizing catalyst system in areactor cascade formed by at least two reactors, one of which is a gasphase reactor and one of which is a loop reactor, said loop reactorbeing operated with an inert hydrocarbon, namely linear or branchedaliphatic C₃-C₆-hydrocarbon. The reactors are operated with differentamounts of hydrogen and comonomers to produce a high molecular weightportion in one of the reactors and a low molecular weight portion in theother, so as to provide a bimodal polyethylene composition comprising arelatively low molecular weight part and relatively high molecularweight part.

In particular, the present invention comprises a process forpolymerising ethylene and comonomer(s) in at least two stages, in aprocess comprising a loop and a gas phase reactor, of which

(i) in the first stage, a low molecular weight, relatively high densitypolymer fraction having a melt flow rate MFR₂ of at least 250 g/10 minis prepared in one or more loop reactor(s) in the presence of anunsupported ethylene-polymerizing catalyst system which comprisestitanium and magnesium as active components, and

(ii) in the second stage, a high molecular weight, relatively lowdensity copolymer is produced in one or more gas phase reactor(s) usingan alpha-olefin, like 1-butene, 1-hexene or 1-octene, as a comonomer.The polymerization conditions are selected so that the final polymer hasa predetermined melt flow rate, preferably so that MFR₅ is 0.7 g/10 minor less.

More specifically, the present process is a process for producingpolyethylene compositions comprising bimodal ethylene homo- andcopolymers in a multistage reaction sequence of successivepolymerization stages in the presence of an ethylene-polymerizingcatalyst system characterized by using an unsupported catalystcomprising magnesium and titanium as active constituents, and carryingout the process in at least one loop polymerization stage and at leastone gas phase polymerization stage, operated with different amounts ofhydrogen and comonomers to produce a high molecular weight portion inone of the polymerization stages and a low molecular weight portion inanother so as to provide a polyethylene composition with the lowmolecular weight part having a MFR₂ of 250 g/10 min or more.

The HD polyethylene film-making process is a process for producing highdensity polyethylene films, comprising producing a polyethylenecomposition in the presence of an ethylene-polymerizing catalyst systemcomprising an unsupported catalyst comprising magnesium and titanium asactive constituents, in a multistage reaction sequence of successivepolymerization stages, at least one of which is a loop polymerizationstage and at least one of which is a gas phase polymerization stage,operated with different amounts of hydrogen and comonomers to produce ahigh molecular weight portion in one of the polymerization stages and alow molecular weight portion in another so as to provide a bimodal highdensity polyethylene with a low molecular weight part having a densityabove 960 kg/m³ and a high molecular weight part, the composition havinga density of 940-965 kg/m³ and MFR₂₁ of 3-50 g/10 min, and blowing saidpolyethylene composition to a film.

The medium density polyethylene film-making process is characterized bya process for preparing medium density polyethylene films, comprisingproducing a polyethylene composition in the presence of anethylene-polymerizing catalyst system comprising an unsupported catalystcomprising magnesium and titanium as active constituents, in amultistage reaction sequence of successive polymerization stages, atleast one of which is a loop polymerization stage and at least one ofwhich is a gas phase polymerization stage, operated with differentamounts of hydrogen and comonomers to produce a high molecular weightportion in one of the polymerization stages and a low molecular weightportion in another so as to provide bimodal medium density polyethylenewith a low molecular weight part having a density of 940-980 kg/m³ and ahigh molecular weight part, the composition having a density of 925-940kg/m³ and MFR₂₁ of 7-30 g/10 min, and blowing said polyethylenecomposition to a film.

The low density polyethylene film-making process is characterized by aprocess for preparing low density polyethylene films, comprisingproducing a polyethylene composition in the presence of anethylene-polymerizing catalyst system comprising an unsupported catalystcomprising magnesium and titanium as active constituents, in amultistage reaction sequence of successive polymerization stages, atleast one of which is a loop polymerization stage and at least one ofwhich is a gas phase polymerization stage, operated with differentamounts of hydrogen and comonomers to produce a high molecular weightportion in one of the polymerization stages and a low molecular weightportion in another so as to provide bimodal low density polyethylenewith a low molecular weight part having a density of 935-960 kg/m³, anda high molecular weight part, the polyethylene composition having adensity of 915-930 and MFR₂₁ of 10-50 g/10 min or more, and blowing saidpolyethylene composition to a film.

An important advantage of the present process is that it providesmaterial for blown films with good mechanical properties and goodappearance in a process where the whole range of PE products from LLD toHD can be produced.

By means of the invention it is possible to produce polyethylenematerial with improved homogeneity without the use of prepolymeriser(unless it is considered otherwise necessary).

The tear strength and good processability on a film line make thepresent materials useful for production of thin films of thicknesses inthe range of 5 μm, or even less than 5 μm to over 30 μm. Films made fromthe materials also exhibit good barrier properties to water vapour.

Next, the invention will be more closely examined with the aid of thefollowing detailed description.

DETAILED DESCRIPTION OF THE INVENTION Definitions

For the purpose of the present invention “loop reactor” designates areactor made of a conduit forming a closed loop and through which thepolymer slurry, where the catalyst and the polymer produced in thereactor are suspended in a fluid phase consisting of diluent, monomer,possible comonomers and hydrogen. The fluid phase may also contain smallamounts of additives, e.g. to reduce the static electricity. The reactormay be operated continuously or intermittently.

By “gas phase reactor” is meant any mechanically mixed or fluidized bedreactor, where polymer particles are suspended in a gas consisting ofmonomer, comonomer(s) and eventually hydrogen and/or inert gas.Preferably the gas phase reactor comprises a mechanically agitatedfluidized bed reactor with gas velocity of at least 0.2 m/s.

“Melt flow rate”, or abbreviated MFR, is a measure of the melt viscosityand thus also of the molecular weight of the polymer. A high value ofMFR corresponds to a low molecular weight. It is measured by pressingthe polymer melt through a standard cylindrical die at a standardtemperature in a special measuring device (melt indexer) equipped with astandard piston under a standard load. For polyethylene, the melt flowrate is measured at 190° C. The abbreviation MFR is usually providedwith a numerical subscript, which indicates the load under which themeasurement was made. Thus, MFR₂ designates that the measurement wasperformed under 2.16 kg load and MFR₂₁ designates that the measurementwas performed under 21.6 kg load. The determination of MFR is describede.g. in ISO 1133 C4, ASTM D 1238 and DIN 53735.

By “flow rate ratio”, or abbreviated FRR, is meant a ratio between twoMFR values measured from the same polymer using different loads. Theabbreviation FRR is usually provided with a numerical subscriptindicating which loads have been used to determine the FRR. Thus,FRR_(21/2) has been calculated as the ratio of MFR₂₁ to MFR₂. The FRR isa measure of the broadness of the molecular weight distribution. A highFRR corresponds to broad molecular weight distribution.

The complex viscosity at G*=5 kPa, η_(5kPa), is measured using a dynamicrheometer. It is the measure of the average molecular weight of thepolymer.

The shear thinning index, SHI_(5/300), is defined as the ratio of theviscosity at G*=5 kPa to the complex viscosity at G*=300 kPa. It is ameasure of the molecular weight distribution.

The storage modulus, G′, at the point where the loss modulus G″ has aspecified value of 5 kPa, denoted as G′_(5 kPa), is also a measure ofmolecular weight distribution. It is sensitive to very high molecularweight polymer fraction.

The Polymer Composition

The present invention concerns a process for producing polyethylenecompositions having a bimodal molar mass distribution comprising arelatively high molar mass portion and a relatively low molar massportion.

The process is especially advantageous for producing ethylene(co)polymer compositions having a broad molecular weight distributionand a high average molecular weight, and in particular compositionswhich are used in applications where homogeneity is important, such asfilm or pipe. Typically, in these compositions the MFR₂ of the lowmolecular weight fraction is higher than 250 g/10 min.

The low molecular weight fraction of the polyethylene compositionproduced with the process according to the present invention has a MFR₂of 250 g/10 min or more, preferably approximately 300-1000 g/10 min. TheMFR₂₁ of the final polymer composition is 50 g/10 min or less.Alternatively or additionally the MFR₅ of the final composition is 0.7g/10 min or less or the MFR₂₁ of the final polymer composition is 20g/10 min or less.

The density of the low molecular weight fraction is typically 935 kg/m³or more, in particular 935-980 kg/m³. The density of the final polymercomposition can vary greatly, since polymer compositions with a densityin the range of 915-965 kg/m³ can be produced with the process of thepresent invention.

The weight fraction of the low molecular weight material should bewithin 5-95% of the final polymer composition. Accordingly, the fractionhaving a relatively high molecular weight should have such averagemolecular weight and comonomer content that the final bimodal ethylenepolymer or copolymer composition has the above-described melt flow rateand density.

According to a preferred embodiment, the ethylene polymer or copolymercomposition produced with the process of the present invention comprisesa low molecular weight part with a density above 960 kg/m³ and a highmolecular weight part, said composition having a density of 940-965kg/m³ and MFR₂₁ of 3-50 g/10 min, preferably 3-15 g/10 min.

The SHI_(5/300) of the composition satisfies the relationship

SHI_(5/300)≦0.00014·η_(5kPa)+78, and

G′_(5kPa) satisfies the relationship

G′_(5kpa)≧28·SHI_(5/300)+425.

According to another preferred embodiment, the ethylene polymer orcopolymer composition produced with the process according to the presentinvention comprises a low molecular weight fraction having a melt flowrate MFR₂ within 300-1000 g/10 min, preferably within 300-600 g/10 minand a density between 960-980 kg/m³. The weight fraction of the lowmolecular weight fraction is within 5-95%, preferably 20-55% and inparticular 35-50% of the final polymer composition. The compositionfurther comprises a high molecular weight fraction, and the finalethylene polymer or copolymer composition has a melt flow rate MFR₂₁within 3-50 g/10 min, preferably within 3-15 g/10 min and a densitywithin 940-965 kg/m³.

The composition described in either one of the two passages above isadvantageously used to produce high density films. Typically, the filmblown from said composition has a dart drop higher than 200 g,preferably over 350 g. The number of gels is typically lower than 50,preferably lower than 20 and in particular lower than 10 according tothe gel determination method presented below.

According to yet another preferred embodiment, the ethylene polymer orcopolymer composition produced with the process according to the presentinvention comprises a low molecular weight fraction having a melt flowrate MFR₂ within 250-1000 g/10 min, preferably within 300-600 g/10 minand a density between 940-980 kg/m³. The weight fraction of lowmolecular weight material is within 20-60%, preferably 30-50% and inparticular 40-50% of the final polymer composition. Said compositionfurther comprises a high molecular weight fraction. The final ethylenepolymer or copolymer composition has a melt flow rate MFR₂₁ within 2-50g/10 min, preferably within 3-15 g/10 min and density within 930-965kg/m³. This kind of composition is advantageously used for manufacturingpipes.

According to another preferred embodiment of the invention, the ethylenepolymer or copolymer composition produced with the process according tothe present invention comprises a low molecular weight fraction having amelt flow rate MFR₂ of 250-1000 g/10 min, preferably 300-500 g/10 minand a density in the range of 940-980 kg/m³. The weight fraction of lowmolecular weight material within 5-95%, preferably 20-50% and inparticular 35-50% of the final polymer composition. The compositionfurther comprises a high molecular weight fraction. The final ethylenepolymer or copolymer composition has a melt flow rate MFR₂₁ within 7-30g/10 min, preferably within 10-25 g/10 min and a density within 925-940kg/m³. This kind of composition is advantageously used for producingmedium density films.

According to still another preferred embodiment of the invention, theethylene polymer or copolymer composition produced with the processaccording to the present invention comprises a low molecular weightfraction having a melt flow rate MFR₂ of 250-1000 g/10 min, preferably300-500 g/10 min an a density in the range of 935-960 kg/m³. The weightfraction of low molecular weight material within 5-95%, preferably20-50% and in particular 35-50% of the final polymer composition. Thecomposition further comprises a high molecular weight fraction. Thefinal ethylene polymer or copolymer composition has a melt flow rateMFR₂₁ within 10-50 g/10 min, preferably within 15-25 g/10 min and adensity within 915-930 kg/m³. This kind of composition is advantageouslyused for producing low density films.

In addition to the polyethylene compositions described above, it isclear that the process according to the present invention is alsosuitable for producing less demanding polyethylene materials having anarrower molecular weight distribution and/or a lower molecular weight.

Polymerization Process

To produce the polymer compositions, ethylene is polymerized in thepresence of a suitable catalyst, preferably a Ziegler-Natta catalyst(cf. below), at an elevated temperature and pressure. Polymerization iscarried out in a cascade comprising polymerization reactors selectedfrom the group of loop and gas phase reactors.

In addition to the actual polymerization reactors used to produce thebimodal ethylene homo- or copolymer, the polymerization reaction systemoptionally comprises a number of additional reactors, such asprereactors. The prereactors include any reactor for prepolymerizing orprecontacting the catalyst or modifying the olefinic feed, if necessary.All reactors of the reactor system are preferably arranged in a cascade.

In the following description the reactor system is described to compriseone loop reactor (referred to as “the first reactor”) and one gas phasereactor (referred to as “the second reactor”), in that order. However,it should be understood that the reactor system can comprise thereactors in any number. In principle, the reactors can also be arrangedin any order. Preferably, however, the loop reactor(s) is arranged priorto the gas phase reactor(s). It is also preferred to produce the lowmolecular weight part of the polymer composition in the loop reactor,and thus prior to the high molecular weight part of the composition.

In every polymerization step it is possible to use also comonomersselected from the group of C₄₋₁₀ olefins, such as 1-butene, 1-pentene,1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene and1-decene. It is also possible to use two or more olefins selected fromsaid group. Preferably a higher alpha-olefin, such as 1-butene,1-hexene, 4-methyl-1-pentene or 1-octene is used. In particular,1-hexene is preferred. It is to be understood that the comonomer usedmay be the same or different in the different reactors. Preferably, thecomonomer is selected so that the boiling point of the comonomer is notclose to the boiling point of the diluent, whereby the diluent recoverybecomes more economical.

The use of comonomers is particularly preferred for the preparation ofthe high molar mass portion. The amount of comonomers in the presentmaterials is generally 0 to 5 wt-%, preferably less than about 2 wt-%.The low molecular weight component contains less than about 1 wt-%comonomers.

According to the invention, the polymerization comprises the steps of

subjecting ethylene, optionally hydrogen and/or comonomers to a firstpolymerization reaction in a first polymerization zone or reactor,

recovering the first polymerization product from the firstpolymerization zone,

feeding the first polymerization product to a second reaction zone orreactor,

feeding additional ethylene and optionally hydrogen and/or comonomers tothe second reaction zone,

subjecting the additional ethylene and optional hydrogen and/orcomonomer to a second polymerization reaction in the presence of thefirst polymerization product to produce a second polymerization product,and

recovering the second polymerization product from the second reactionzone.

Thus, in the first step of the process, ethylene with the optionalcomonomer(s) together with the catalyst is fed into the firstpolymerization reactor. Along with these components hydrogen as a molarmass regulator is fed into the reactor in the amount required forachieving the desired molar mass of the polymer. Alternatively, the feedof the first reactor can consist of the reaction mixture from a previousreactor, if any, together with added fresh monomer, optional hydrogenand/or comonomer and cocatalyst. In the presence of the catalyst,ethylene and the optional comonomer will polymerize and form a productin particulate form, i.e. polymer particles, which are suspended in thefluid circulated in the reactor.

The polymerization medium typically comprises the monomer (i.e.ethylene) and/or a hydrocarbon diluent, and optionally hydrogen and/orcomonomers. According to the invention, the hydrocarbon diluent mainlycomprises a C₃-C₆ aliphatic linear or branched hydrocarbon or a mixtureof two or more of these. Thus, the diluent can be selected from a groupcomprising propane, n-butane, isobutane, n-pentane, 2-methyl butane,2,2-dimethyl propane, hexane, 2-methyl pentane, 3-methyl pentane,2,2-dimethyl butane, 2,3-dimethyl butane and 2-ethyl butane. Inparticular propane is suitable to be used as a diluent, since it allowsthe operation in supercritical conditions at a relatively lowtemperature. According to a preferred embodiment of the invention, aC₄₋₆ aliphatic hydrocarbon, such as n-butane, pentane or hexane, and inparticular isobutane is used to further improve the homogeneity of thematerial. According to another preferred embodiment, isobutane, n-butaneor isopentane is used. It should be noted, that the diluent may alsocontain minor amounts of lighter and/or heavier hydrocarbons which aretypically found in industrially used hydrocarbon fractions. It ispreferred to use light diluents, such as propane, n-butane or isobutane,since these can readily be separated from the polymer.

The polymer is circulated continuously through the loop reactor by meansof a circulation pump or by other means of circulation.

The conditions of the loop reactor are selected so that at least 5 wt-%,preferably at least 20 wt-%, most preferably at least 35 wt-%, of thewhole production is produced in the loop reactor(s). The temperature isin the range of 40 to 110° C., preferably in the range of 70 to 100° C.The reaction pressure is in the range of 25 to 100 bar, preferably 35 to80 bar.

In loop polymerization more than one reactor can be used in series. Insuch a case the polymer suspension in an inert hydrocarbon produced inthe loop reactor is fed without separation of inert components andmonomers either intermittently or continuously to the following loopreactor, which is operated at a lower pressure than the previous loopreactor.

The polymerization heat is removed by cooling the reactor by a coolingjacket. The residence time in the loop reactor must be at least 10minutes, preferably 20-100 min for obtaining a sufficient yield ofpolymer.

As discussed above, hydrogen is fed into the reactor to control themolecular weight of the polymer. Hydrogen is added to the reactor sothat the molar ratio of hydrogen to ethylene in the fluid phase of thereactor is at least 100 mol H₂/kmol ethylene, preferably 300-600 molH₂/kmol ethylene. It should be noted that the exact amount of hydrogendepends on the desired molecular weight (or MFR) of the polymer producedin the first stage, and thus no exact value can be given.

Comonomer can be introduced into the loop reactor to control the densityof the polymer produced in the first polymerization stage. If the finalethylene (co)polymer should have a high density above 940 kg/m³, themolar ratio of the comonomer to the ethylene should be at most 200 molcomonomer/kmol ethylene. If the final ethylene (co)polymer should have alow density below 930 kg/m³, the molar ratio of the comonomer to theethylene should be between 200-1000 mol comonomer/kmol ethylene,preferably between 300-800 mol comonomer/kmol ethylene. Again, it shouldbe noted that the exact amount of comonomer depends on the desiredcomonomer content (or density) of the polymer produced in the firststage, and thus no exact value can be given.

If the density of the ethylene (co)polymer produced in the loop reactoris higher than 960 kg/m³, it is advantageous to perform thepolymerization in supercritical conditions, above the criticaltemperature and critical pressure of the fluid which forms the reactionmixture. Typically, the temperature then exceeds 90° C. and the pressureexceeds 55 bar.

The pressure of the first polymerization product including the reactionmedium is reduced after the first reaction zone in order to evaporatevolatile components of the product, e.g. in a flash tank. As a result ofthe flashing, the product stream containing the polyethylene is freedfrom hydrogen and can be subjected to a second polymerization in thepresence of additional ethylene to produce a high molar mass polymer.

The second reactor is preferably a gas phase reactor, wherein ethyleneand preferably comonomers are polymerized in a gaseous reaction medium.

The gas phase reactor is typically an ordinary fluidized bed reactor,although other types of gas phase reactors can be used. In a fluidizedbed reactor, the bed consists of the growing polymer particles from thefirst reaction zone and/or the polymer particles formed in the bed ofthe gas phase reactor, as well as the active catalyst which is dispersedwithin the growing polymer particles. The bed is kept in a fluidizedstate by introducing gaseous components, for instance monomer on aflowing rate which will make the particles act as a fluid. Typicallyfluidizing gas is introduced into the bed from the bottom through afluidization grid. The fluidizing gas consists of monomer and optionallycomonomer(s) and/or hydrogen and/or inert gases, like nitrogen, propane,n-butane or isobutane. The fluidizing gas can contain also inert carriergases, like nitrogen and propane and also hydrogen as a molecular weightmodifier. The fluidized gas phase reactor can be equipped with amechanical mixer.

In order to produce the high molecular weight component in the gas phasereactor, hydrogen can be added into the reactor to control the molecularweight of the final polymer. The concentration of hydrogen in thefluidizing gas shall be such that the molar ratio of hydrogen toethylene is lower than 100 mol hydrogen/kmol ethylene, preferably lowerthan 50 mol/kmol. It should be noted that the exact amount of hydrogendepends on the desired MFR of the final ethylene (co)polymer, and thusno exact value can be given.

Comonomer can also be introduced into the gas phase reactor to controlthe density of the final ethylene (co)polymer. For example, if the finalethylene (co)polymer should have a high density above 940 kg/m³, themolar ratio of the comonomer to the ethylene should be at most 400 molcomonomer/kmol ethylene. If the final ethylene (co)polymer should have alow density below 930 kg/m³, the molar ratio of the comonomer to theethylene should be between 200-1000 mol comonomer/kmol ethylene,preferably between 300-800 mol comonomer/kmol ethylene. Again, it shouldbe noted that the exact amount of comonomer depends on the desiredcomonomer content or density of the final ethylene (co)polymer, and thusno exact value can be given.

The gas phase reactor used can be operated in the temperature range of50 to 115° C., preferably between 60 and 110° C. The reaction pressureis typically between 10 and 40 bar and the partial pressure of monomerbetween 1 and 20 bar.

The pressure of the second polymerization product including the gaseousreaction medium can then be released after the second reactor in orderoptionally to separate part of the gaseous and possible volatilecomponents of the product, e.g. in a flash tank. The overhead stream orpart of it is recirculated to the gas phase reaction zone.

The production split between the relatively high molar masspolymerization reactor and the relatively low molar mass polymerizationreactor is 5-95:95-5. Preferably, 20 to 50%, in particular 35 to 50%, ofthe ethylene homopolymer or copolymer is produced at conditions toprovide a polymer having a MFR₂ of 250 g/10 min or more and constitutingthe low molar mass portion of the polymer, and 95 to 50%, in particular90 to 50%, of the ethylene homopolymer or preferably copolymer isproduced at such conditions that the final polymer has an MFR₂₁ of 50g/10 min or less, in particular about 3 to 50 g/10 min and constitutingthe high molar mass portion of the polymer.

Catalyst

The catalyst used in the process according to the invention is aZiegler-Natta catalyst consisting of magnesium and titanium as activemetals and aluminium as the chlorinating agent. The catalyst is usedunsupported. By “unsupported” it is meant that all the components of thecatalyst are catalytically active, and thus no deposition of the activecomponents to a specific carrier (e.g. an inorganic oxide) has beenmade.

According to a preferred embodiment of the invention, the catalyst isprepared as follows: The magnesium complex (B) needed in preparation ofthe catalyst is prepared by reacting a suitable alcohol (C) with amagnesium compound (D).

The alcohol (C) must be such that the complex (B) is soluble innon-polar hydrocarbon diluent. For this reason, the hydroxy group of thealcohol should be sterically hindered. Suitable examples of suchalcohols are linear or branched C₄-C₁₀ alcohols, in particular1-alcohols with a hydrocarbyl, preferably methyl and in particular ethylor propyl, substituent in the second carbon atom. In particular,2-ethyl-1-hexanol and 2-propyl-1-pentanol are preferred.

The magnesium compound (D) is a dialkyl magnesium. The two alkyl groupsare independently methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl oroctyl. Suitable examples of such compounds are dibutyl magnesium (DBM),butyl ethyl magnesium (BEM) and butyl octyl magnesium (BOMAG).

The molar ratio of the alcohol (C) to the magnesium compound (D) shouldbe within the range of 1.7-2.1, preferably 1.8-2.0.

The magnesium complex (B) is then reacted with an alkyl metal chloride(A) to form magnesium chloride-aluminium complex (E). Thus, the alkylmetal chloride (A) must have a sufficient chlorinating power for this tohappen. Alkyl metal chloride has the general formula (I):

R_(n)MeCl_(3-n)  (I)

wherein each R is independently C₁-C₁₀, preferably C₁-C₄ alkyl, Me is ametal of group 13 in the Periodic Table of Elements, preferably Al or B,in particular aluminium and n is an integer 1 or 2. Preferred example ofcompound (A) is ethyl aluminium dichloride.

The ratio between the magnesium complex (B) and alkyl metal chloridecompound (A) should be such that the ratio of chlorine atoms in thecompound (A) to the magnesium atoms in complex (B) is between 1 and 2.5,preferably 1.7-2.3. If the ratio is less than 1, the chlorination shallbe incomplete. On the other hand, a ratio higher than 2.5 isunnecessary, since complete chlorination is obtained at ratio 2.

The solid catalyst component is then prepared by reacting the magnesiumchloride-metal complex (E) with a titanium chloride compound (F). Thetitanium compound (F) may in addition to titanium and chloride containalkoxy groups, according to the general formula:

TiCl_(m)(OR)_(4-m)  (II)

wherein m is an integer from 1 to 4, and in each OR-group independentlyR is linear or branched aliphatic hydrocarbyl comprising 1-12,preferably 1-4, carbon atoms. Examples of suitable titanium compounds(F) are Ti(OC₂H₅)Cl₃, Ti(OC₂H₅)₂Cl₂ and Ti(OC₂H₅)₃Cl, most preferred istitanium tetrachloride, TiCl₄.

The amount of titanium compound (F) is such that the molar ratio ofcompound (F) to complex (B) is between 1:1.5-1:3, preferably between1:1.75-1:2.25.

The solid catalyst component may then be washed and dried, as it isknown in the art. The washing will remove the impurities possiblyremaining in catalyst particles which would have an adverse effect onthe activity of the catalyst.

The composition of the thus obtained catalyst is preferably such thataluminium (when Me is aluminium) is present in 1-2 wt-%, magnesium in8-12 wt-%, titanium in 7-10 wt-% and chlorine in 45-55 wt-%.

Blending and Compounding

The polymer obtained from the reactor is in the form of powder.Generally, the film blowers are not able to use the polymer in thepowder form. The powder is transformed to pellets in a compounding stepwhere the polymer is first mixed with additives, like antioxidants andprocess stabilisers, then melt homogenised in an extruder and finallypelletised.

The extruder used in the compounding can be of any type known in theart. It may be either a single screw extruder which contains only onescrew or a twin screw extruder which contains two parallel screws, or acombination of these. Preferably a twin screw extruder is used.

The twin screw extruder may be of either corotating or counterrotatingtype. In a corotating twin screw extruder the screws rotate in the samedirection while in a counterrotating twin screw extruder the screwsrotate in the opposite directions. The counterrotating twin screwextruder has the advantage of giving better homogeneity on a certainlevel of specific energy input. On the other hand, corotating twin screwextruder generally degrades the polymer less on a certain level ofspecific energy input.

The films are prepared by running the pelletized product into a film ona film line. The die diameter is typically 100-300, in particular140-200 mm, and the die gap is 1-2 mm, for HD films typicallyapproximately 1.5 mm. The blow-up ratio (BUR), which is the ratio of thediameter of the expanded film bubble to the die diameter, may be 1-10,typically between 2 and 4, and for HD films in particular 4. For HDfilms the frost line height is usually between 5 and 10 die diameters(DD) and for LLD films between 0 and 4, in particular 2 and 4 DD.Preferably, the material exhibits a neck contraction, so that theeffective blow-up ratio (BUR_(eff)), which is the ratio of the diameterof the expanded film bubble to the narrowest diameter of the neck,exceeds the BUR based on the die diameter.

Thus, if BUR is about 4, then BUR_(eff) is preferably higher than 5. Thethickness of the films prepared according to the present invention istypically 3 μm-100 μm. Thus, it is possible to make thin films of 3-50μm, in particular 5-30 μm thickness.

The film prepared from the material produced by the process describedabove has a dart drop of more than 200 g, preferably more than 350 g,tear strength in machine and transverse directions at least 0.1 N, andat least 0.5 N, preferably 1 N or more, respectively. The goodhomogeneity is manifested by the low amount of gels in an area ofA4-size; typically the films prepared according to the invention exhibitgels less than 50, preferably less than 20 and in particular 10 or lessin an area of A4 size.

Description of Analytical Methods

Tear Strength

Tear strength is measured according to ISO 6383. The force required topropagate tearing across a film specimen was measured using a pendulumdevice. The pendulum swings by gravity through an arc tearing thespecimen from a precut slit. The specimen is held on one side by thependulum and on the other side by a stationary member. Tear strength isthe force required to tear the specimen.

Gel Count

The film sample (of size A4) was investigated under polarized light andcounted. The number of gels per A4 size was then given as the result.

Dart Drop

Dart drop is measured using the ISO 7765-1 method. A dart with a 38 mmdiameter hemispherical head is dropped from a height of 0.66 m onto afilm clamped over a hole. If the specimen fails, the weight of the dartis reduced and if it does not fail the weight is increased. At least 20specimen need to be tested. A weight resulting failure of 50% of thespecimen is calculated.

Rheological Measurements

The rheology of polymers has been determined using Rheometrics RDA IIDynamic Rheometer. The measurements have been carried out at 190° C.temperature under nitrogen atmosphere. The measurements give storagemodulus (G′) and loss modulus (G″) together with absolute value ofcomplex viscosity (η*) as a function of frequency (ω) or absolute valueof complex modulus (G*).

$\eta^{*} = \frac{\sqrt{\left( {G^{\prime 2} + G^{\prime\prime 2}} \right)}}{\varpi}$

 G*={square root over ((G′²+G″²))}

According to Cox-Merz rule complex viscosity function, η*(ω) is the sameas conventional viscosity function (viscosity as a function of shearrate), if frequency is taken in rad/s. If this empiric equation is validabsolute value of complex modulus corresponds shear stress inconventional (that is steady state) viscosity measurements. This meansthat function η*(G*) is the same as viscosity as a function of shearstress.

In the present method viscosity at a low shear stress or η* at a low G*(which serve as an approximation of so called zero viscosity) is used asa measure of average molecular weight. On the other hand, shearthinning, that is the decrease of viscosity with G*, gets morepronounced the broader is molecular weight distribution. This propertycan be approximated by defining a so called shear thinning index, SHI,as a ratio of viscosities at two different shear stresses.

Thus:

SHI_(5/300)=η*₅/η*₃₀₀

wherein

η*₅ is complex viscosity at G*=5 kPa and

η*₃₀₀ is complex viscosity at G*=300 kPa

As mentioned above storage modulus function, G′(ω), and loss modulusfunction, G″(ω), are obtained as primary functions from dynamicmeasurements. The value of the storage modulus at a specific value ofloss modulus increase with broadness of molecular weight distribution.However this quantity is highly dependent on the shape of molecularweight distribution of the polymer.

EXAMPLES Example 1

Preparation of Complex

8.6 g (66.4 mmol) of 2-ethyl-1-hexanol was added slowly to 27.8 g (33.2mmol) of 19.9 wt-% butyl-octyl-magnesium. The reaction temperature waskept below 35° C. This complex was used in the catalyst preparation.

Preparation of Catalyst

5.3 g (5.1 mmol) of the above prepared complex was added slowly to 4.7ml (5.1 mmol) of 20 wt-% EADC, and the mixture was stirred for 12 hoursat 25° C. Then, 0.48 g (2.6 mmol) of titanium tetrachloride was addedand the mixture was stirred for one hour at 40-50° C. The catalyst waswashed with pentane and dried for two hours at 40-50° C.

Composition of the catalyst was: Al 1.4%, Mg 9.5%, Ti 8.9%, Cl 47.2%

Test Polymerization

The above catalyst was tested in ethylene homopolymerization. Hydrogenwas measured into a 3 litre autoclave from a 500 ml cylinder so, thatthe pressure in the cylinder was reduced by 500 kPa. 1.8 l of n-pentanewas introduced into the reactor and the temperature was adjusted to 90°C. A measured amount of the above-mentioned catalyst andtriethylaluminium cocatalyst (molar ratio of Al/Ti was 15 mol/mol) wasintroduced into the reactor and ethylene feed was started via thehydrogen measuring cylinder. The reactor was maintained at a constantpressure of 14.4 kPa by continuously introducing ethylene into thereactor (partial pressure of ethylene was 4.4 kPa). The polymerizationwas continued for one hour, after which the reactor was evacuated, andthe polymer was recovered and dried.

The productivity of the catalyst in polymerization was 69 kg PE/gcatalyst, the melt flow rate MFR₂ was 0.5 g/10 min and the bulk density320 kg/m³.

Example 2

A pilot plant comprising a loop and a gas phase reactor was operated sothat ethylene, propane diluent and hydrogen were introduced into a loopreactor together with a commercially available non-supported catalystsold under trade name Lynx760 by Mallinkrodt. The operating temperatureof the reactor was 95° C. and pressure 60 bar. Ethylene homopolymer wasproduced at a rate of 24 kg per hour and the MFR₂ of the polymer afterthe loop reactor was 600 g/10 min. Thus, the low molecular weightcomponent was made in the loop reactor. The density of the polymer wasnot measured, but prior experience has indicated that a homopolymer ofthis MFR has a density of about 974 kg/m³. The polymer slurry waswithdrawn from the reactor and introduced into a separation stage wherethe hydrocarbons were removed from the polymer. The polymer containingthe active catalyst was transferred into a gas phase reactor, whereadditional ethylene, hydrogen and 1-butene comonomer were added. Thepolymerization was thus continued to produce the high molecular weightcomponent so that a polymer composition having a density of 945 kg/m³and the MFR₂₁ of 6.3 g/10 min. The polymer was withdrawn from the gasphase reactor at a rate of 59 kg per hour. The polymer was pelletisedusing a corotating twin screw extruder and analysed.

The pelletized product was then run into a film on a film line havingdie diameter 160 mm and die gap 1.5 mm. The blow-up ratio (BUR) was 4and the frost line height equal to 8 die diameters (DD). The resultingfilm had neck of 150 mm (corresponding to an effective blow-up ratioBUR_(eff) of 4.3), dart drop of 360 g, tear strength in machine andtransverse directions 0.11 and 1.0 N respectively and 5 gels in an areaof A4-size.

Comparative Example 1

A pilot plant comprising a loop and a gas phase reactor was operatedaccording to Example 1, with the exception that a catalyst preparedaccording to Example 3 of PCT Patent Application WO-A-95/35323 was used.Catalyst feed was 15 g per hour. Ethylene homopolymer was produced at arate of 28 kg per hour and the MFR₂ of the polymer after the loopreactor was 380 g/10 min.

Polymer was withdrawn from the gas phase reactor at a rate of 67 kg perhour. The MFR₂₁ of the final product was 9.7 g/10 min and the densitywas 945 kg/ m³.

The pelletized product was then run into a film as disclosed inExample 1. The film had neck of 135 mm, dart drop of 170 g, tearstrength in machine and transverse directions 0.15 and 0.45 Nrespectively and 220 gels in an area of A4-size.

Comparative Example 2

A unimodal material produced using a Cr-catalyst (sold by Borealis undera trade name HE6960) was run into a film in a similar fashion than inExample 1. The material had MFR₂₁ 8 g/10 min and density 945 kg/ m³.

The resulting film had neck of 110 mm, dart drop of 150 g, tear strengthin machine and transverse directions 0.2 and 0.5 N respectively and 10gels in an area of A4-size.

What is claimed is:
 1. A process for producing polyethylene compositionscomprising bimodal ethylene homo- and copolymers in a multistagereaction sequence of successive polymerization stages in the presence ofan ethylene-polymerizing catalyst system, said process comprisingcarrying out the process in at least one loop polymerization stage andat least one gas phase polymerization stage, operated with differentamounts of hydrogen and comonomers to produce a high molecular weightportion in one of the polymerization stages and a low molecular weightportion in another to produce a polyethylene composition with the lowmolecular weight part having a MFR₂ of 250 g/10 min or more, whereinsaid catalyst system comprises an unsupported catalyst comprisingmagnesium and titanium as active constituents.
 2. The process accordingto claim 1, comprising subjecting ethylene, optionally together withhydrogen and/or comonomers, in the presence of an unsupported catalystsystem comprising magnesium and titanium as active constituents to aloop polymerization or copolymerization reaction in a first reactionzone or reactor to produce a polymer having a MFR₂ of 250 g/10 min ormore, recovering the first polymerization product from the firstpolymerization zone, feeding the first polymerization product to a gasphase zone or reactor, feeding additional ethylene and optionallyhydrogen and/or comonomers to the gas phase reaction zone, subjectingthe additional ethylene and optionally additional monomer(s) andhydrogen to a second polymerization reaction in the presence of thefirst polymerization product to produce a second polymerization producthaving a MFR₂₁ of 50 g/10 min or less, and recovering the combinedpolymerization product from the gas phase reaction zone.
 3. The processaccording to claim 1 or 2, wherein the catalyst is prepared by reactingan alcohol (C) with a magnesium compound (D) in order to obtain amagnesium complex (B), reacting an alkyl metal compound (A) with saidmagnesium complex (B) to form a magnesium chloride-metal complex (E),reacting the magnesium chloride-aluminium complex (E) with a titaniumcompound (F) in order to prepare a solid catalyst component, andoptionally washing and drying the solid catalyst component.
 4. Theprocess according to claim 3, wherein the alcohol (C) comprises2-ethyl-1-hexanol or 2-propyl-1-pentanol, or a mixture thereof.
 5. Theprocess according to claim 3, wherein the magnesium compound (D)comprises dialkyl magnesium, or a mixture thereof.
 6. The processaccording to claim 3, wherein the molar ratio of the alcohol (C) to themagnesium compound (D) is in the range of 1.7-2.1.
 7. The processaccording to claim 3, wherein the alkyl metal compound (A) has thegeneral formula: R_(n)MeCl_(3−n) wherein each R is independently C₁-C₁₀alkyl, Me is a metal of Group 13 in the Periodic Table of Elements, andn is an integer of 1 or
 2. 8. The process according to claim 7, whereinthe alkyl metal compound (A) is an aluminum dichloride.
 9. The processaccording to claim 3, wherein the ratio of chlorine atoms in thecompound (A) to the magnesium atoms in complex (B) is between 1 and 2.5.10. The process according to claim 3, wherein the titanium compound (F)has the general formula TiCl_(n)(OR)_(4−n) wherein n is an integer from1 to 4, and in each OR group independently R is linear or branchedsaturated hydrocarbyl comprising 1-12 carbon atoms.
 11. The processaccording to claim 10, wherein the titanium compound (F) is titaniumtetrachloride.
 12. The process according to claim 3, wherein the molarratio of the titanium compound (F) to complex (B) is between 1:1.5-1:3.13. The process according to claim 1, wherein the loop reactor isoperated using a diluent selected from the group of linear or branchedC₄-C₆-hydrocarbons and mixtures thereof.
 14. The process according toclaim 13, wherein the diluent is isobutane, n-butane, isopentane or amixture thereof.
 15. The process according to claim 1, wherein thecomonomer is C₄-C₁₀ olefin, or a mixture thereof.
 16. The processaccording to claim 1, wherein the density of the low molecular weightpart is 960-980 kg/m³ and the density of the final polymer compositionis 940-965 kg/m³.
 17. The process according to claim 16, wherein theMFR₂ of the low molecular weight component is 300-1000 g/10 min and theMFR₂₁ of the final polymer composition is 3-50 g/10 min.
 18. The processaccording to claim 16 or 17, wherein 5 to 95 wt-% of the ethylenehomopolymer or copolymer is produced at conditions which provide apolymer having a MFR₂ of 300-1000 g/10 min.
 19. The process according toclaim 1, wherein the density of the low molecular weight part is 940-980kg/m³ and the density of the final polymer composition is 930-965 kg/m³.20. The process according to claim 19, wherein the MFR₂ of the lowmolecular weight part is 250-1000 g/10 min and the MFR₂₁ of the finalpolymer composition is 2-50 g/10 min.
 21. The process according to claim19 or 20, wherein 20-60 wt-% of the ethylene homopolymer or copolymer isproduced at conditions to provide a polymer having a MFR₂ of 250-1000g/10 min.
 22. The process according to claim 1, wherein the density ofthe low molecular weight part is 940-980 kg/m³ and the density of thefinal polymer composition is 925-940 kg/m³.
 23. The process according toclaim 22, wherein the MFR₂ of the low molecular weight component is250-1000 g/10 min and the MFR₂₁ of the final polymer composition is 7-30g/10 min.
 24. The process according to claim 22 or 23, wherein 5-95 wt-%of the ethylene homopolymer or copolymer is produced at conditions toprovide a polymer having a MFR₂ of 250-1000 g/10 min.
 25. The processaccording to claim 1, wherein the density of the low molecular weightpart is 935-960 kg/m³ and the density of the final polymer compositionis 915-930 kg/m³.
 26. The process according to claim 25, wherein theMFR₂ of the low molecular part is 250-1000 g/10 min and the MFR₂₁ of thefinal polymer composition is 10-50 g/10 min.
 27. The process accordingto claim 25 or 26, wherein 5-95 wt-% of the ethylene homopolymer orcopolymer is produced at conditions to provide a polymer having a MFR₂of 250-1000 g/10 min.
 28. The process according to claim 1, wherein thefinal polymer composition has a MFR₅ of 0.7 g/10 min or less.
 29. Theprocess according to claim 1, wherein the final polymer composition hasa MFR₂₁ of 20 g/10 min or less.
 30. A process for producing high densitypolyethylene films, comprising producing a polyethylene composition inthe presence of an ethylene-polymerizing catalyst system comprising anunsupported catalyst comprising magnesium and titanium as activeconstituents, in a multistage reaction sequence of successivepolymerization stages, at least one of which is a loop polymerizationstage and at least one of which is a gas phase polymerization stage,operated with different amounts of hydrogen and comonomers to produce ahigh molecular weight portion in one of the polymerization stages and alow molecular weight portion in another so as to provide a bimodal highdensity polyethylene with a low molecular weight part having a densityabove 960 kg/m³ and a high molecular weight part, the composition havinga density of 940-965 kg/m³ and MFR₂₁ of 3-50 g/10 min, and blowing saidpolyethylene composition to a film.
 31. A process for preparing mediumdensity polyethylene films, comprising producing a polyethylenecomposition in the presence of an ethylene-polymerizing catalyst systemcomprising an unsupported catalyst comprising magnesium and titanium asactive constituents, in a multistage reaction sequence of successivepolymerization stages, at least one of which is a loop polymerizationstage and at least one of which is a gas phase polymerization stage,operated with different amounts of hydrogen and comonomers to produce ahigh molecular weight portion in one of the polymerization stages and alow molecular weight portion in another so as to provide bimodal mediumdensity polyethylene with a low molecular weight part having a densityof 940-980 kg/m³ and a high molecular weight part, the compositionhaving a density of 925-940 kg/m³ and MFR₂₁ of 7-30 g/10 min, andblowing said polyethylene composition to a film.
 32. A process forpreparing low density polyethylene films, comprising producing apolyethylene composition in the presence of an ethylene-polymerizingcatalyst system comprising an unsupported catalyst comprising magnesiumand titanium as active constituents, in a multistage reaction sequenceof successive polymerization stages, at least one of which is a looppolymerization stage and at least one of which is a gas phasepolymerization stage, operated with different amounts of hydrogen andcomonomers to produce a high molecular weight portion in one of thepolymerization stages and a low molecular weight portion in another soas to provide bimodal low density polyethylene with a low molecularweight part having a density of 935-960 kg/m³, and a high molecularweight part, the polyethylene composition having a density of 915-930and MFR₂₁ of 10-50 g/10 min or more, and blowing said polyethylenecomposition to a film.
 33. The process according to any of claims 30-32,wherein the polyethylene composition is compounded and pelletized priorto blowing it to a film.
 34. The process according to claim 30, whereinthe film exhibits a number of gels lower than 50 in an area of A4 size.35. The process according to claim 30, wherein a film with a thicknessof 5-100 μm is produced.
 36. The process according to claim 30, whereinthe film has a dart drop higher than 200 g.
 37. The process according toclaim 7, wherein said Me is aluminum.
 38. The process according to claim17, wherein said MFR₂ of the low molecular weight component is 300-600g/10 min.
 39. The process according to claim 17, wherein said MFR₂₁ ofthe final polymer composition is 3-15 g/10 min.
 40. The processaccording to claim 18, wherein 20 to 55 wt-% of said ethylenehomopolymer or copolymer is produced at conditions which provide apolymer having a MFR₂ of 300-1000 g/10 min.
 41. The process according toclaim 18, wherein 35-50 wt-% of said ethylene homopolymer or copolymeris produced at conditions which provide a polymer having a MFR₂ of300-1000 g/10 min.
 42. The process according to claim 20, wherein theMFR₂ of the low molecular weight part is 300-600 g/10 min.
 43. Theprocess according to claim 20, wherein said MFR₂₁ of the final polymercomposition is 3-15 g/10 min.
 44. The process according to claim 21,wherein 30-50 wt-% of the ethylene homopolymer or copolymer is producedat conditions to provide a polymer having a MFR₂ of 250-1000 g/10 min.45. The process according to claim 21, wherein 40-50 wt-% of theethylene homopolymer or copolymer is produced at conditions to provide apolymer having a MFR₂ of 250-1000 g/10 min.
 46. The process according toclaim 23, wherein the MFR₂ of the low molecular weight component is300-500 g/10 min.
 47. The process according to claim 23, wherein saidMFR₂₁ of the final polymer composition is 10-25 g/10 min.
 48. Theprocess according to claim 24, wherein 20-50 wt-% of the ethylenehomopolymer or copolymer is produced at conditions to provide a polymerhaving a MFR₂ of 250-1000 g/10 min.
 49. The process according to claim24, wherein 35-50 wt-% of the ethylene homopolymer or copolymer isproduced at conditions to provide a polymer having a MFR₂ of 250-1000g/10 min.
 50. The process according to claim 26, wherein said MFR₂ ofthe low molecular part is 300-500 g/10 min.
 51. The process according toclaim 26, wherein said MFR₂₁ of the final polymer composition is 15-25g/10 min.
 52. The process according to claim 27, wherein 20-50 wt-% ofthe ethylene homopolymer or copolymer is produced at conditions toprovide a polymer having a MFR₂ of 250-1000 g/10 min.
 53. The processaccording to claim 27, wherein 35-50 wt-% of the ethylene homopolymer orcopolymer is produced at conditions to provide a polymer having a MFR₂of 250-1000 g/10 min.
 54. The process according to claim 1, wherein saiddifferent amounts of hydrogen and comonomers is at least 100 molhydrogen/kmol ethylene in said loop reactor and less than 100 molehydrogen/kmol ethylene in said gas phase reactor.
 55. The processaccording to claim 30, wherein said different amounts of hydrogen andcomonomers is at least 100 mol hydrogen/kmol ethylene in said loopreactor and less than 100 mole hydrogen/kmol ethylene in said gas phasereactor.
 56. The process according to claim 31, wherein said differentamounts of hydrogen and comonomers is at least 100 mol hydrogen/kmolethylene in said loop reactor and less than 100 mole hydrogen/kmolethylene in said gas phase reactor.
 57. The process according to claim32, wherein said different amounts of hydrogen and comonomers is atleast 100 mol hydrogen/kmol ethylene in said loop reactor and less than100 mole hydrogen/kmol ethylene in said gas phase reactor.